The compound (2R,3S,24S) -2,3-diacetoxy-22,23-epoxy-24-ethyl-.beta.-homo-7-oxa-5.alpha.-cholestan-6 -one, having formula 1 of the drawings which is the subject matter of our co-pending Indian Applicaiton No.IP 389/Del/96 is a novel compound useful as an intermediate in the synthesis of homobrassinolide having molecular formula C.sub.29 H.sub.50 O.sub.6 and isomeric structural formulae 8 and 9 which are highly potent plant growth promoters. The compound of formula 1 is prepared by a process which comprises dihydroxylating (22E, 24S)-24-ethyl-5.alpha.-cholestan-2, 22-diene-6-one, having formula 10 of the drawings in a mixture of chlorinated solvents and tert-butanol in presence of tetradecyltrimethylammonium permanganate (TDTAP) reagent at temperature ranging from -5 to 30.degree. C., for one to two hours and separating the resultant compound having structural formula 11 as shown in the accompanying drawings the from the reaction mixture by column chromatography method, acetylating the compound of formula 11 of the drawings to obtain compound of formula 12 of the drawings by slowly adding trifuloroperoxyacetic acid in presence of disodium hydrogen phosphate as a buffer at 0 to 30.degree. C. for a period ranging between 14-18 hours to get compound of the formula 1 of the drawings in 67% yield and the said compound of the formula 1 of the drawings is separated from the reaction mixture by column chromatography. The compound of formula 1 of the drawings when treated with lithium bromide in the presence of a highly acidic sulphonated cation exchange resin and acetonitrile as a solvent, furnishes a compound having molecular formula C.sub.33 H.sub.53 Bro.sub.7 and isomeric structural formulae 2 and, the compound having molecular formula C.sub.33 H.sub.53 Bro.sub.7 and structural formulae (2R, 3S, 24S) -2, 3- diacetoxy-22-bromo-24-ethyl-.beta.-homo-7-oxa-22- hydroxy-5.alpha.-cholestan-6-one of formula 2 of the drawings and the compound having structural formula (2R, 3S, 24S) -2-3-diacetoxy-23-bromo-24- ethyl-.beta.- homo-7-oxa -22-hydroxy-5.alpha.-cholestan -6-one of formula 3 shown in the drawings accompanying this specification, when subject to acetylation, corresponding bromotriacetate having molecular formula C.sub.35 E.sub.55 Bro.sub.8 is obtained and the bromotriacetate is obtained is further subjected to solvolysis using aqueous acetic acid at elevated temperatures so as to obtain respective hydroxytriacetate having molecular formula C.sub.35 H.sub.56 O.sub.9 and the structural formulae 4 and 5 as shown in the accompanying drawings. The said compounds of formulae 4 and 5 as shown in the accompanying drawings when subjected to acetylation with acetic anhydride and pyridine give a tetraacetate compound having molecular formula C.sub.37 H.sub.58 O.sub.10 and structural formulae 6 and 7 as shown in the drawings accompanying this specification.
Compounds of formula 6 and formula 7 as shown in the drawings can be separated by column chromatography and after alkaline hydrolysis followed by acidification, produce compounds of formula 8 and formula 9 respectively. Compounds of formula 8 and formula 9 are the structural isomers of homobrassinolide and both the isomers are highly potent plant growth promoters. The compound (2R, 3S, 24S)-2-3, diacetoxy-22,23-epoxy-24-ethyl -.beta.- homo-7- oxa-5 -cholestan-6-one-having formula 1 can be synthesised from stigmasterol.
Although both the compounds of formulae 8 and 9 are potent plant growth promoters, compound 8 is much more active compared to compound 9. Hence, the main objective of the present invention is to develop a convenient process for the preparation of compound having molecular formula C.sub.29 H.sub.5 O.sub.6 in high ratio (61:39) of compound of formula 8 to compound of formula 9.